In a drive control, it is known to move a load mass L by a shaft W or a transmission G using a controlled drive or motor M. It is irrelevant whether the motor M or the load L has a linear or a rotary movement, and whether the transmission G converts a rotary movement into a linear movement or translatory movement, or vice versa, or whether rotary movements are transmitted to linear movements, and linear movements are transmitted to rotary movements. The two illustrations according to FIG. 1 and FIG. 2 show two possible drive configurations. FIG. 3 shows a block diagram of a model of the associated controlled system in which a setpoint value (a) is predefined at the input end for a controller 1. An actual value (b), which is proportional to a torque from which the motor rotational speed (c) is obtained by integration 2, and the motor position (d) is obtained by further integration 3 which is then set up at the output end. The elasticity of the shaft W or of a transmission G is taken into account by means of a spring component 4. The output value (e) corresponds to the spring moment which reacts on the motor rotational speed (integrator 2) via the additional point 2′. The spring moment (e) is logically linked to a load torque (f). The load rotational-speed actual value (g) is obtained from this by further integration 5, and the load position actual value (h) is obtained by further integration 6. Said load position actual value (h) is fed back 4′ negatively to the spring component 4 at the input end.
While the following is limited to rotary movements for the sake of illustration, it also applies in the same way to linear or mixed linear/rotary movements.
Under specific conditions of motor inertia, load inertia, and the elasticity of the shaft W and/or of the transmission G, low frequency oscillations occur between the motor M and load L. These are referred to below as load oscillations which are frequently very destructive and very difficult to control in terms of control technology. Frequently, in systems which are capable of oscillation, state controllers are used for damping such load oscillations. These controllers are generally so complex that they can only be applied by academic control specialists. Accordingly, these state controllers are unsuitable for a wide-ranging product solution, especially with a view to simple actuation.
Another known solution uses a difference rotational-speed feedback and difference position feedback to the torque's setpoint value of the motor M. In addition, a superimposed motor rotational-speed controller also supplies a torque setpoint value which is added to the difference rotational-speed feedback and difference position feedback. This results in a complex structure similar to that of the classic state controller which is difficult to set. While the motor rotational-speed controller compensates the feedback values to a certain extent, the setting of the motor rotational-speed controller generally has a strong influence on the effect of the connection.
One way of avoiding this could be to control the load rotational speed directly without a motor rotational-speed controller. However, this is also problematic because the controlled system has three poles at the edge of stability and does not have any zero point, which makes stable control possible only within a very narrow band. It is noted here that there is also a further pole at the edge of stability as a result of an I-component of the controller which makes actuation difficult.
If no measures for actively damping load oscillations are taken, excitation of the oscillation must be avoided by controlling the movement. The result of this is that the movement processes take a comparatively long time, and that only a small degree of control compliance can be achieved. Interference can then excite oscillations which are not actively damped.